Alternate route telephone switching mechanism



'Dec. 2, 1947. R. E. HERSEY ALTERNATE ROUTE TELEPHONE SWITCHING MECHAN ISM Filed May 15, 1945 INVENTOR R. E HERSEV BY C. MW

ATTORNEY Patented Dec. 2, 1947 ALTERNATE ROUTE TELEPHONE SWITCHING MECHANISM Ralph E. Hersey, Madison, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application May 15, 1945, Serial No. 593,957

11 Claims. 1

This invention relates to telephone systems and more particularly to systems employing automatic switching mechanisms under common control.

In such systems connections between subscribers lines terminating in different offices are established over groups of interoffice trunks. Arrangements have heretofore been suggested whereby, when a group of interofiice trunks is insufiicient to carry the calls directed thereover, a part of the calls are routed over trunks leading to a tandem point where they are completed to the desired ofiice.

The present invention is more particularly directed to the type of telephone system disclosed in Patent No. 1,862,549, granted June 14, 1932, to R. Raymond and W. J. Scully, in which panel type switches, known as district and ofiice selectors are used for selecting a trunk to a wanted oflilce. These selectors are operated under the control of register senders, which receive the wanted line designation as dialed by the callin subscriber. When the ofilce code has been received, the sender summons a decoder and transmits to it the ofiice code. The decoder translates this code and returns to the sender an indication of the selections to be made, the nature of the called ofiice and other information required for the completion of the call.

Plans heretofore proposed for the alternate routing of interofiic traflic from panel type dial ofi'ices have employed considerable equipment individual to the trunk groups which is effective to switch from the normal route to the alternate route before all of the trunks of the normal route become busy and have therefore resulted in unnecessary rerouting.

In accordance with the present invention each decoder is equipped with means'for testing trunk groups of such a nature that plurality of decoders may test a line group simultaneously.

The testing means of the invention operates a direct route relay if there are idle trunks available and an alternate route relay if no idle trunks appear available, means being provided individual to the direct trunk group to simulate one busy trunk for a predetermined interval after a trunk group is tested.

Means is also provided for varying the length of time for simulating the busy trunk in accordance with the size and location of th trunk group.

These and other features of the invention will be more apparent from a consideration of the following detailed description taken in connec- 2 tion with the accompanying drawing which shows in schematic form a calling and a called subscriber's line with panel type switching equipment for establishing a connection between them, together with a sender, decoder-connector and parts of two decoders, only the circuits embodying the invention having been shown in detail.

For a complete disclosure of a telephone system to which the present invention relates, reference may be made to the above-mentioned patent to Raymond and Scully, while a tandem office, suitable for use in the alternate route, is disclosed in Patent 1,840,132, granted January 5, 1932, to T. I-LRoberts.

Assuming that the subscriber at substation I00 wishes to talk with the subscriber at substation I 50, he removes his receiver to originate the call. In response to the removal of the receiver the line finder I0! is automatically operated to connect with the calling line, while the district finder I02 and sender selector I03 are also operated to extend the line I00 to the sender I30. The subscriber now dials the number of the substation I50, which is made up of the code designation of the oflice I33 at which the line l 50 is located and the numerical designation of the line.

When the code designation has been recorded on the code registers represented by relays I04, I05 and I06, the decoder-connector I01 is operated to connect the sender I30 with an idle decoder, for example, decoder I3I. The code registers of the decoder, represented by relays I08, I09 and H0 then take the code registration from the sender.

All these operations take place as described in the Raymond-Scully patent. However, instead of immediately operating a route relay in response to the translation performed by the code registers as takes place in the above patent, an intermediate or code relay such as relay H2 or H3 is operated. Relay H2 is shown associated with a group of trunks leading to the wanted ofiice while relay H3 is shown associated with a group of trunks leading to an intermediate office. Either one of these code relays may be operated as a result of dialing the appropriate code, but since it was assumed that the code of office I33 was dialed, code relay II2 will be operated.

Included in each decoder is a set of test relays I26, I21, I28, etc. sufficient in number to test the largest group of trunks. When a code relay operates, it connects the sleeve conductors of the group of trunks associated with that code to the windings of the test relays. Busy trunks have ground connected to their sleeve conductors from the district selector circuit, so that the test relays I26, I21, I28, etc. connected with busy trunks are operated. Where there are fewer trunks in a group than the number of test relays, the code relay connects direct ground to the test relays not connected to a trunk. This is illustrated by relay II2, where two of the trunks outgoing to oflice I33 are shown connected over the two inner contact of relay I I2 to the windings of relays I21 and I28 whil direct ground is connected over the third contact of relay I I2 to the Winding of relay I26. Assuming that the two trunks indicated are idle, relays I21 and I28 will not operate, but relay I26 will be operated by the ground supplied by relay I I2. A circuit is closed through the upper winding of relay I29 through resistances I36, I31, I38, and I39 to ground as soon as the decoder I 3I is seized. When relay I26 operates it short-circuits resistance I36, reducing the resistance in series with the upper winding of relay I29 by that amount. However, relay I29 is so adjusted that it will operate only in series with a single resistance such as resistances I36, I31, etc. and does not operate at this time.

When relay I49 operates, a measured time interval after the operation of relay II2,since relay I29 has not operated, a circuit is closed from ground, over the lower contact of relay I49, inner lower contact of relay I29, to battery through the lower winding of relay I29 and over the fourth contact of relay I I2 to the winding of direct route relay I I4. Route relay I I4 performs the functions of a route relay as described in the Raymond- Sculley patent, transmitting to the sender the necessary informationto permit it to control district selector I45, ofiice selector I46, incoming selector I41 and final selector I43'and complete the connection to the called line I59.

The code register relays I68 to -I I6, code relay II2, route relay I I4 and test relays I26 to I28 all release when the decoder releases in the usual manner.

If all of the trunks outgoing to office I33 had been busy, resistances I36, I31 and I38 would have been short-circuited, leaving only resistance I39 in series with the winding of relay I29, causing relay I29 to operate. I When relay I46 operates under this condition, it closes a circuit from ground over its lower contact, front contact of relay I29, fifth contact of relay II2 to the winding of route relay I Iwhich is the alternate route relay for the direct route relay I I4. Relay II5 transmits the necessary information to the sender to cause it to select brush set I5I of the district selector and to employ that brush set to extend the connection by way of office selector I52 to intermediate ofiice I53 from which it is extended to oilice I33 and over incoming selector I54 and final selector I55 to the called line.

There may be other omce codes, for example, one which operates code relay II3 for which the route by way of office I53 will represent the first choice or most direct route. In that case route relay I92, which is operated in response to testing the trunks to ofiice I53 will transmit the same information to the sender for controlling the district and office selections but would transmit different information for controlling the extension of the call from ofi1ce'I53 toward the wanted office.

Each trunk groupis provided with a test recording relay which is effective to maintain an indication for a predetermined time'after the test.

Each time that the trunk group associated with code relay I I2 is tested, and relay I29 is not operated, a circuit is closed from ground at the lower back contact of relay I29, front contact of relay I46, lower front contact of relay I I2 to the winding of relay II1 and battery. Relay II1 operates and looks over its upper contact to ground at the back contact .of relay IIB. At its lower contact; relay II1 disconnects ground "from in shunt of condenser I24 and permits that condenser to charge from +l10-volt battery through resistance I25. At its lower front contact, relay I I1 connects groundto the winding of relay I I8 which is connected to the anode of gas-filled tube II9. As condenser I-24'gradually charges it increases the potential onthe control anode I22 of the tube II9 to a point where the control gap breaks down causing'the 'mainl gap to flash and operate relay IIB. Relay .I I8 in operating releases relay I I1 which discharges the timing condenser. Resistance I25 is indicated as variable-since it may be set at different values to control the time which is to be consumed in charging the condenser I25 in accordance with the size'and location of the trunk group.

If this same group of trunks is again seized for test while relay'I I1'is locked, theoperation of code relay 'I'I2 closes'a circuit'from battery through the winding of relay I'4I, back contact of relay I40, lowest contact of rela I I2, upper contact of relay II1 to ground atthe back contact of relay II6. Relay I'4I operates in-this circuit and short-circuits resistance I 39. If at this time there is only one idle trunk in the group, that trunk will be seized asa result of the-trunk'test which operated relay II 1 and is not available for this second call. Relay I29 operates, and causes'the operation of alternate routerelay II5to direct'this call over the alternate'route. After relay II1 releases, relay I29 can onlyoperate if 'all of'the trunks are busy. Relay I61 and tube I69 are'individual to the group'of trunks outgoing to office I53 and similar relays areprovided for each trunk group.

The circuit previously-traced to the lower winding of relay I29 in parallel'with the operating circuit for the direct route relay opposes that through the upper winding. Since the circuit is open at the time that relay I29 normally operates it does not interfere withthat operation. Furthermore, after relay I29 has operated, thecircuit' is opened at the contact of relay I29"so that it has no tendency to "falsely release'relay I29. Its chief value appears at a time when the 'seizure'of an.additional trunk "might cause the operation of relay I29 in the'middlejof a test andlinterfere with the operation of the route relay. Such a time might be when two trunks'are idle,but one will be seized because of a prior test as indicated by the operation ofrelay II1. Under'thiscondition.relay I29 will not operate, but if the vprior call seizes its trunk before the route relay has been operated and this marker released, another resistance would be short+circuite'd, leaving only one in series with relay I29 and tending to operate relay I29. However, under this condition .the circuit through the lower winding is of sufficient strength to neutralize the current through the upper winding and hold the'back contacts closed.

It will .be noted that thisarrangementis such that two decoders.suchasdecoders I3I and I32 cantest a trunk group at the .same time since the grounded sleeve conductors merely operate two test relays inparallel.

Whatis claimed is:

1. In atelephone exchange system, a calling office, called onices, an intermediate ofiice, switching mechanism located in said calling ofiice, a group of direct trunks extending from said switching mechanism to each of said called ofiices, a group of trunks extending from said switching mechanism to said intermediate oflice over which connections may be further extended to said called offices, a plurality of control means in said calling ofiice each including a code relay and a route relay for each called oifice and means responsive to the operation of said route relay for controlling said switching mechanism to seize a trunk leading to the corresponding oifice, trunk testing means in said control means, means responsive to the operation of a code relay in one of said control means for connecting said trunk testing means with the trunks extending to the corresponding oifice, means effective to operate the route relay of the corresponding oifice if one of said'trunks is idle, and, means to simulate to said trunk testing means a busy condition of one of said trunks for a predetermined time after the operation of said route relay.

2. In a telephone exchange system, a calling ofiice, called oiiices, an intermediate ofiice, switching mechanism located in said calling oifice, a group of direct trunks extending from said switching mechanism to each of said called ofiices, a group of trunks extending from said switching mechanism to said intermediate office over which connections may be further extended to said called oifices, a plurality of control means in said calling ofiice each including a code relay and a route relay for each called oflice and means responsive to the operation of said route relay for controlling said switching mechanism to seize a trunk leading to the corresponding oflice, trunk testing means in said control means, means responsive to the operation of code relay in one of said control means for connecting said trunk testing means with the trunks extending to the corresponding ofiice, means efiective to operate the route relay of the corresponding office if one of said trunks is idle, a relay individual to said trunk group, means to operate said individual relay under the control of said code relay, timing means, means to lock said relay under the control of said timing means, and means under the control of said individual relay to simulate to said trunk testing means a busy condition of one of said trunks after the operation of said route relay for a time interval measured by said timing means.

3. In a telephone exchange system, a calling office, called offices, an intermediate ofiice, switching mechanism located in said calling office, a group of direct trunks extending from said switching mechanism to each of said called oifices, a, group of trunks extending from said switching mechanism to said intermediate office over which connections may be further extended to said called ofiices, a plurality of control means in said calling office each including a code relay and a route relay for each called ofiice and means responsive to the operation of said route relay for controlling said switching mechanism to seize a trunk leading to the corresponding office, trunk testing means in said control means, means responsive to the operation of the code relay of a particular ofiice in a plurality of said control means for simultaneously connecting the trunk testing means of said plurality of control means to the group of trunks extending to said particular ofiice, and means effective in each control means to operate the route relay of said particular oflice.

4. In a telephone exchange system, a calling oflice, called offices, an intermediate ofiice, switching mechanism located in said calling oflice, a group of direct trunks extending from said switching mechanism to each of said called ofiices, a group of trunks extending from said switching mechanism to said intermediate ofiice over which connections may be further extended to said called offices, a plurality of control means in said calling ofiice each including a code relay and a route relay for each called office and means responsive to the operation of said route relay for controlling said switching mechanism to seize a trunk leading to the corresponding ofiice, trunk testing means in said control means, means responsive to the operation of the code relay of a particular office in a plurality of said control means for simultaneously connecting the trunk testing means of said plurality of control means to the group of trunks extending to said par ticular office, means effective in each control means to operate the route relay of said particular ofiice, means individual to said group of trunks to simulate a busy condition of one trunk, and means responsive to the connection of said group of trunks to the testing means in any one of said control means for rendering said busy simulating means effective.

5. In a telephone exchange system, a calling office, called offices, an intermediate oflice, switching mechanism located in said calling ofiice, a group of direct trunks extending from said switching mechanism to each of said called offices, a group of trunks extending from said switching mechanism to said intermediate oifice over which connection may be further extended to said called oflices, a plurality of control means in said calling oflice each including a code relay and a route relay for each called ofiice and means responsive to the operation of said route relay for controlling said switching mechanism to seize a trunk leading to the corresponding ofiice, trunk testing means in said control means, means responsive to the operation of the code relay of a particular oifice in a plurality of said control means for simultaneously connecting the trunk testing means of said plurality of control means to the group of trunks extending to said particular office, means effective in each control means to operate the route relay of said particular oifice, means individual to said group of trunks to simulate a busy condition of one trunk and means responsive to the connection of said group of trunks to the testing means in any one of said control means for rendering said busy simulating means effective, and means for holding said busy simulating means operated for a predetermined length of time.

6. In a telephone exchange system, a calling ofiice, called oflices, an intermediate oiflce, switching mechanism located in said calling oflice, a group of direct trunks extending from said switching mechanism to each of said called offices, a group of trunks extending from said switching mechanism to said intermediate ofiice over which connections may be further extended to said called ofiices, a plurality of control means in said calling ofiice, each including a code relay and a route relay for each called office and means responsive to the operation of said route relay for controlling said switching mechanism to seize a trunk leading to the corresponding oince, trunk testing means in said control means, means responsive to the operation of a code relay in one of said control means for connecting said trunk testing means with the trunks extending to the corresponding office, means effective to operate the route relay of the corresponding officeif one of said trunks is idle, a relay llldlvidual'to said trunk group, means to'o'perate said individual relay under the control of said code re-' lay, timing means, means to lock said relay under the control of said timing means, means under thecontrol of said individual relay to simulate a" busy condition of one ofsaid trunks after the operation of said route relay for a time interval measured by said timing means, and means to adjust said timing means to provide different predetermined times for different'trunk' groups.

'7; ma telephone exchange system, a, calling ofiice, called offices, an intermediate ofiice, switching mechanism located in said calling oifice, a

group of direct trunks extending from saidswitching mechanismto each of said called offices, a group of trunks extending from said switching mechanism to said intermediate oiiice over'which connection may be furtherextende'd to said called offices, a plurality of control means in said calling office each including a code relay and a route relay for each called ofiice and means responsive to the operation of said route relay for controlling said switching mechanism to seize a trunk leading to the corresponding ofiice, trunk testing means in said control means, means responsive to the operation of the code relay of a particular office in a plurality of said control means for simultaneously connecting the trunk testing means of said plurality of control means to the group of trunks extending to said particular office, means eiiective in each control means to operate the route relay of said particular office, means individual to said group of trunks to simulate a busy condition of one trunk, and means responsiv to the connection of said group of trunks to the testing means in any of said control means for rendering said busy simulating means effective, means for holding said busy simulating means operated for a predetermined length of time, and means to adjust said timing means to provide difierent predetermined times for different trunk groups.

8. In a telephone exchange system, a calling oflice, called oilices, an intermediate oflice, switch ing mechanism located in said calling office, a

group of direct trunks extending from said switching mechanism to each of said called offices,-

.a group of trunks extending from said switching mechanism to said intermediate office over which connections may be further extended to said called oflices', a plurality of control means in said calling ofiice each including a code relay and a relay operative when all of said trunk resistances are'short-circuited, means under the control of said marginal relay to operate the route relay of the corresponding ofilce if at least one of saidtrlinks is idle, means to operate a different route relay if said marginal relay is operated,- and" means'to simulate a busy condition of one of said trunks for a predetermined time after the opeiatioii ofsaid route relay by short-circuitingsaid auxiliary resistance.

9 In' a telephone exchange system, a calling ofiice, called ofiices, an intermediate ofiice, switching mechanism located in said calling office, a

ofiices, a group of trunks extending from said switching mechanism to said intermediate ofiic'e over which connections may be further extendedto saidcalled ofiices, a plurality of control meansin saidcalli ng' office-each including a code relay and a route relay for each called oifice and meansresponsive to the operation of said route relay for controlling said switching mechanism to seize a tru'nkleading to the corresponding ofiice, trunkte'sting means in said control means including a resistance for each trunk and anauxiliary re-' sistance arranged in series, means responsive to theoper'ation of a code relay in one of saidcontrol means for connecting said trunk testingmeans with the trunks extending'to the corresponding ofiice and for short-circuiting the resistances associated with busy trunks, a marginal relay operative when all of said trunk resistances are shortacirc'uited, means under the control of said'marginal relay to operate the'route relay of the corresponding office if at-least one of said trunks is idle, means to operate a different route relay if said marginal relay is operated, a relay individual to said trunk group, means to operate said individual relay under the control of said code relay, timing means, means to lock said relay under the control of said timing means,-

and means under the control of said individual relay to simulate a busy condition of one of saidtrunks after the operation of said route relay by short-circuiting said auxiliary resistance for a time interval measured by said timing means.

10. In a; telephone exchange system, a, calling.

oiiice, called oflices, an intermediate oiiice', switchingmechanism locatedin said calling oific'e, a

group of direct trunks extending from said switching mechanism to each of said called ofiices, a group of trunks extending from said switching mechanism to said intermediate ofiice over which connections may be further extended to said called offices, a plurality of control means in said calling oflice each'including a code relay and aroute relay for each called ofiice and means responsive to the operation of said route relay for controlling said switching'mechanism to seize a trunk leading to the corresponding office, trunk testing means in said control means-including a resistance for each trunk and an auxiliary resistance arranged in series, means responsive to the operation'of a code relay in one of said control means for connecting said trunk testing means with the trunks extending to the corresponding ofiice and for short-circuiting the resistances associated with busy trunks, a marginalrelay operative when all of said trunk resistances are short-circuited, means effective a predetermined time after the operation of said code relay under the control of said marginal relay to operate the route relay of the corresponding office if at least one of said trunks is idle, means to operate a different route relay if said marginal relay is operated, means to simu latea busy condition of one of said trunks for a predetermined time after the operation of said route relay by short-circuiting said auxiliary resistance, and means under the control of said route-relay operating means for preventing the subsequent operation of said marginal relay.

1 In a telephone exchange system, a calling office, called ofiices, an intermediate oifice, switching mechanism located in said calling oflice, a group of direct trunks extending from said switching mechanism to each of said called ofiices, a group of trunks extending from said switching mechanism to said intermediate office over which connections may be further extended to said called offices, a plurality of control means in said calling office each including a code relay and a route relay for each called ofiice and means responsive to the operation of said route relay for controlling said switching mechanism to seize a trunk leading to the corresponding oflice, trunk testing means in said control means including a resistance for each trunk and an auxiliary resistance arranged in series, means responsive to the operation of a code relay in one of said control means for connecting said trunk testing means with the trunks extending to the corresponding oflice and for short-circuiting the resistance associated with busy trunks, a marginal relay operative when all of said trunk resistances are short-circuited, means eifective a predetermined time after the operation of said code relay under the control of said marginal relay to operate the route relay of the corresponding office if at least one of said trunks is idle, means to operate a different route relay if said marginal relay is operated, a relay individual to said trunk group, means to operate said individual relay under the control of said code relay, timing means, means to lock said relay under the control of said timing means, means under the control of said individual relay to simulate a busy condition of one of said trunks after the operation of said route relay by short-circuiting said auxiliary resistance for a time interval measured by said timing means, and means under the control of said route relay operating means for preventing the subsequent operation of said marginal relay.

RALPH E. HERSEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Gillings Mar, 14, 1933 King Apr. 8, 1941 Number 

